U.S. patent application number 14/411977 was filed with the patent office on 2015-06-18 for tire shape inspection method and tire shape inspection device.
The applicant listed for this patent is KABUSHIKI KAISHA KOBE SEIKO SHO (KOBE STEEL, LTD.). Invention is credited to Masato Kannaka, Eiji Takahashi, Toshiyuki Tsuji.
Application Number | 20150168267 14/411977 |
Document ID | / |
Family ID | 50237056 |
Filed Date | 2015-06-18 |
United States Patent
Application |
20150168267 |
Kind Code |
A1 |
Takahashi; Eiji ; et
al. |
June 18, 2015 |
TIRE SHAPE INSPECTION METHOD AND TIRE SHAPE INSPECTION DEVICE
Abstract
A tire shape inspection method comprises a contact face
acquisition step of acquiring contact face height changes by
removing data outside of a prescribed range from detected tread
face height data, a height change interpolation step of
interpolating the section removed in the previous step using
heights in the prescribed height range and acquiring height changes
in the interpolated contact faces, and a runout value acquisition
step of acquiring, as a runout value indicating the shape of the
tread face, the difference between the maximum value and the
minimum value in the height changes of the interpolated contact
faces.
Inventors: |
Takahashi; Eiji; (Kobe-shi,
JP) ; Tsuji; Toshiyuki; (Kobe-shi, JP) ;
Kannaka; Masato; (Kobe-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA KOBE SEIKO SHO (KOBE STEEL, LTD.) |
Kobe-shi, Hyogo |
|
JP |
|
|
Family ID: |
50237056 |
Appl. No.: |
14/411977 |
Filed: |
August 28, 2013 |
PCT Filed: |
August 28, 2013 |
PCT NO: |
PCT/JP2013/072991 |
371 Date: |
December 30, 2014 |
Current U.S.
Class: |
356/606 |
Current CPC
Class: |
G01B 11/2408 20130101;
G01B 21/045 20130101; G01B 11/22 20130101; G01B 11/0608 20130101;
G01B 11/25 20130101; G01M 17/027 20130101; G01B 11/24 20130101 |
International
Class: |
G01M 17/02 20060101
G01M017/02; G01B 11/25 20060101 G01B011/25 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 4, 2012 |
JP |
2012-194205 |
Claims
1. A tire shape inspection method that inspects a shape of a tread
face formed of protruding blocks having contact faces formed at top
portions of the protruding blocks and recessed grooves arranged
between the protruding blocks by detecting height data of the tread
face, the method comprising: a contact face acquisition step of
acquiring height changes of the contact faces by removing height
data outside of a prescribed height range from the detected height
data of the tread face, the prescribed height range including an
average value of the detected height data; a height change
interpolation step of interpolating the section of the height data
removed in the contact face acquisition step by using heights in
the prescribed height range in the height changes of the contact
faces acquired in the contact face acquisition step, and acquiring
the interpolated height changes of the contact faces; and a runout
value acquisition step of acquiring, as a runout value indicating
the shape of the tread face, the difference between the maximum
value and the minimum value in the interpolated height changes of
the contact faces.
2. The tire shape inspection method according to claim 1, wherein
the height data of the tread face is detected on a detection line
along a circumferential direction of the tire.
3. The tire shape inspection method according to claim 2, wherein
the height data of the tread face is detected on a plurality of the
detection lines, and wherein a plurality of the runout values are
acquired by repeating the contact face acquisition step, the height
change interpolation step, and the runout value acquisition step
every detected height data of the tread face, and the position of
the detection line with the highest reproducibility of the acquired
runout value is determined as the position of the detection line
for acquiring the runout value indicating the shape of the tread
face of a tire which is a subject to be inspected.
4. The tire shape inspection method according to claim 1, further
comprising: a mask image generation step of capturing an image of
line light on the tread face, the line light which is formed of
sheet light irradiated on the tread face, acquiring an image of the
tread face as an area image by applying triangulation to the
captured line light, detecting boundary lines, which are the
contours of the protruding blocks, in the acquired area image, and
generating a mask image indicating the positions of the boundary
lines, wherein the height data of the tread face is detected from
the area image that is masked with the mask image generated in the
mask image generation step, and wherein the runout value is
acquired by applying the contact face acquisition step, the height
change interpolation step, and the runout value acquisition step to
the detected height data of the tread face.
5. The tire shape inspection method according to claim 1, wherein,
when the runout value indicating the shape of the tread face is
acquired in the runout value acquisition step, the interpolated
height changes of the contact faces, which have been smoothed by
using a low pass filter, are used.
6. The tire shape inspection method according to claim 1, wherein
the prescribed height range used in the contact face acquisition
step is set by using a standard deviation of a distribution of the
height data.
7. A tire shape inspection device that inspects a shape of a tread
face formed of protruding blocks having contact faces formed at top
portions of the protruding blocks and recessed grooves arranged
between the protruding blocks by detecting height data of the tread
face, the device comprising: a contact face acquisition portion
that acquires height changes of the contact faces by removing
height data outside of a prescribed height range from the detected
height data of the tread face, the prescribed height range
including an average value of the detected height data; a height
change interpolation portion that interpolates the section of the
height data removed in the contact face acquisition step by using
heights in the prescribed height range in the height changes of the
contact faces acquired by the contact face acquisition portion, and
acquires the interpolated height changes of the contact faces; and
a runout value acquisition portion that acquires, as a runout value
indicating the shape of the tread face, the difference between the
maximum value and the minimum value in the interpolated height
changes of the contact faces.
Description
TECHNICAL FIELD
[0001] The present invention relates to an inspection technology of
a tire, and more particularly relates to a tire shape inspection
method and a tire shape inspection device for inspecting the shape
of a tread face being a contact face by using a method of image
processing.
BACKGROUND ART
[0002] A tire has a complicated structure in which various
materials, such as rubber, chemical fiber, and steel cord, are
stacked. At a contact face (tread face) having such a complicated
structure, uniformity of the tire radius has to be ensured and
undulation (runout) of the contact face has to be restricted to
prevent vertical vibration (radial runout) caused by a variation in
tire radius.
[0003] Hence, occurrence of a runout is prevented in a
manufacturing phase of a tire, and a runout of the contact face is
inspected for a manufactured tire. In this inspection, a tire
determined to have a large runout is removed from subjects to be
shipped.
[0004] Owing to this, in a final step of tire manufacturing
(inspection step after tire vulcanization), in particular, a runout
at a tread face is measured and a shape defect at a sidewall face
is inspected. A tread face of a tire has a tread pattern having
protruding blocks forming contact faces and recessed grooves.
Hence, when a runout at a tread face is measured, the heights of
the protruding blocks at the contact faces have to be properly
detected.
[0005] In recent years, for a technology of measuring a runout at
such a tread face, there has been developed automation using an
image inspection or the like with a laser distance sensor, a
three-dimensional shape measurement device, or a camera.
[0006] For example, PTL 1 discloses a device for measuring the
outer shape of a subject having bulges and dents at a surface. This
device includes an optical displacement meter that provides
scanning on a prescribed measurement portion of a subject, signal
correction means for, in response to an output signal of the
optical displacement meter, removing a prescribed signal pattern
component from the output signal, and measurement means for
measuring a prescribed shape based on a signal corrected by the
signal correction means.
[0007] This shape measuring device evaluates a signal pattern
component to be removed, by using a parameter based on an
inclination of a signal pattern appearing in sampling data.
CITATION LIST
Patent Literature
[0008] PTL 1: Japanese Unexamined Patent Application Publication
No. 62-232507
SUMMARY OF INVENTION
Technical Problem
[0009] PTL 1 describes that the tire shape detecting device can
measure the outer shape of a tire without selecting a measuring
line even if unnecessary bulges and dents are present on the
surface of the tire, and can acquire correct measurement data at
high speed.
[0010] To determine the signal pattern component to be removed with
high accuracy in the sampling data by the tire shape detecting
device, the parameter value based on the inclination of the signal
pattern has to be properly set. However, since the parameter used
in PTL 1 includes several kinds of parameters, it is a troublesome
work to properly set the plurality of parameters for bulged and
dented shapes which vary depending on the kind of tire. A good
detection result may not be always obtained.
[0011] Also, when the tire shape detecting device in PTL 1 is
applied to a tread face of a tire with many grooves like a winter
tire, which has been widely spread in recent years, reproducibility
of a measurement result obtained on a single measuring line is low
and it is difficult to increase the reproducibility of the
measurement result even if the plurality of parameter values are
changed in various ways.
[0012] In light of the situation, an object of the invention is to
provide a tire shape inspection method and a tire shape inspection
device that can easily obtain measurement results with high
reproducibility.
Solution to Problem
[0013] To attain the above-described object, the invention provides
technical means as follows.
[0014] A tire shape inspection method according to the invention
inspects a shape of a tread face formed of protruding blocks having
contact faces formed at top portions of the protruding blocks and
recessed grooves arranged between the protruding blocks by
detecting height data of the tread face. The method includes a
contact face acquisition step of acquiring height changes of the
contact faces by removing height data outside of a prescribed
height range from the detected height data of the tread face, the
prescribed height range including an average value of the detected
height data; a height change interpolation step of interpolating
the section of the height data removed in the contact face
acquisition step by using heights in the prescribed height range in
the height changes of the contact faces acquired in the contact
face acquisition step, and acquiring the interpolated height
changes of the contact faces; and a runout value acquisition step
of acquiring, as a runout value indicating the shape of the tread
face, the difference between the maximum value and the minimum
value in the interpolated height changes of the contact faces.
[0015] Preferably, the height data of the tread face may be
detected on a detection line along a circumferential direction of
the tire.
[0016] Preferably, the height data of the tread face may be
detected on a plurality of the detection lines. Also, a plurality
of the runout values may be acquired by repeating the contact face
acquisition step, the height change interpolation step, and the
runout value acquisition step every detected height data of the
tread face, and the position of the detection line with the highest
reproducibility of the acquired runout value may be determined as
the position of the detection line for acquiring the runout value
indicating the shape of the tread face of a tire which is a subject
to be inspected.
[0017] Preferably, the method may further include a mask image
generation step of capturing an image of line light on the tread
face, the line light which is formed of sheet light irradiated on
the tread face, acquiring an image of the tread face as an area
image by applying triangulation to the captured line light,
detecting boundary lines, which are the contours of the protruding
blocks, in the acquired area image, and generating a mask image
indicating the positions of the boundary lines. The height data of
the tread face may be detected from the area image that is masked
with the mask image generated in the mask image generation step.
The runout value is acquired by applying the contact face
acquisition step, the height change interpolation step, and the
runout value acquisition step to the detected height data of the
tread face.
[0018] In this case, when the runout value indicating the shape of
the tread face is acquired in the runout value acquisition step,
the interpolated height changes of the contact faces, which have
been smoothed by using a low-pass filter, may be used.
[0019] Also, the prescribed height range used in the contact face
acquisition step may be set by using a standard deviation of a
distribution of the height data.
[0020] A tire shape inspection device according to the invention
inspects a shape of a tread face formed of protruding blocks having
contact faces formed at top portions of the protruding blocks and
recessed grooves arranged between the protruding blocks by
detecting height data of the tread face. The device includes a
contact face acquisition portion that acquires height changes of
the contact faces by removing height data outside of a prescribed
height range from the detected height data of the tread face, the
prescribed height range including an average value of the detected
height data; a height change interpolation portion that
interpolates the section of the height data removed by the contact
face acquisition portion by using heights in the prescribed height
range in the height changes of the contact faces acquired in the
contact face acquisition step, and acquires the interpolated height
changes of the contact faces; and a runout value acquisition
portion that acquires, as a runout value indicating the shape of
the tread face, the difference between the maximum value and the
minimum value in the interpolated height changes of the contact
faces.
Advantageous Effects of Invention
[0021] With the tire shape inspection method and the tire shape
inspection device according to the invention, measurement results
with high reproducibility can be easily obtained.
BRIEF DESCRIPTION OF DRAWINGS
[0022] Part (a) in FIG. 1 is a brief diagram showing a
configuration of a tire shape inspection device according to an
embodiment of the invention, and part (b) is a schematic
illustration showing three-dimensional arrangement of a sport light
irradiation portion and a light position detection portion in a
sensor unit included in the tire shape inspection device.
[0023] FIG. 2 is schematic illustrations showing the external shape
of a tire, part (a) showing a sidewall face, part (b) showing a
tread face.
[0024] FIG. 3 is a schematic illustration showing a tread pattern
of a tire.
[0025] FIG. 4 is a graph showing height changes over the entire
circumference of the tread pattern detected by the tire shape
inspection device according to this embodiment.
[0026] FIG. 5 is an enlarged view showing part of the graph
indicating the height changes over the entire circumference of the
tread pattern in an enlarged manner.
[0027] FIG. 6 is an illustration explaining a method of acquiring
height changes of contact faces from the height changes of the
tread pattern.
[0028] FIG. 7 is an illustration explaining a method of acquiring
runout values from the acquired height changes of the contact
faces.
[0029] FIG. 8 is an illustration showing a graph evaluating
reproducibility of runout values on a plurality of different
detection lines.
DESCRIPTION OF EMBODIMENTS
[0030] An embodiment of the invention is described below with
reference to the drawings.
[0031] A tire shape inspection device 1 according to an embodiment
of the invention detects a displacement in height (height
displacement) of a tire surface by detecting reflection light of
spot light irradiated on the surface (tire surface) of a rotating
tire T by a light receiving element. The tire shape inspection
device 1 detects the height of a tread face and the height of a
sidewall face over the entire circumference among the tire surface,
and acquires a detected displacement amount of the tire surface
(height displacement amount) as a runout value indicating the shape
of the tire surface. The shape of the tire surface is evaluated
according to the runout value acquired as described above, and thus
the shape of the tire T is inspected.
[0032] In case of the shape inspection for the tire T, the tread
face where contact faces are formed, and the sidewall face where
graphic symbols of a brand and the like are formed can be subjects
to be inspected. In this embodiment, however, the tire shape
inspection device 1 that inspects the tread face as a subject to be
inspected is described.
[0033] A configuration of the tire T which is a subject to be
inspected is described with reference to parts (a) and (b) in FIG.
2.
[0034] FIG. 2 is a schematic illustration showing an external shape
of the tire T. Part (a) in FIG. 2 shows a sidewall face of the tire
T. Part (b) shows a tread face of the tire T. The tire T includes
two sidewall faces arranged substantially perpendicularly to a road
face, and a tread face connecting the two sidewall faces. As it is
known, the tread face surrounding the outer circumference of the
tire T is a surface curved to bulge toward the outer side in a
radial direction of the tire. The tread face has a plurality of
protruding blocks (protruding blocks) B forming contact faces at
top portions of the protruding blocks B facing the outer side in
the radial direction of the tire, and recessed grooves arranged
between the plurality of protruding blocks B.
[0035] FIG. 3 shows part of the curved tread face in plan. The
tread face of the tire T has markedly different patterns for a
summer tire and a winter tire. The tread face shown in FIG. 3 has
more grooves than those of a summer tire, and hence is a winter
tire.
[0036] As described above, the tread face of the tire T has the
plurality of protruding blocks B having contact faces, and the
plurality of recessed grooves formed between the plurality of
protruding blocks B and in each block B. FIG. 3 is a front view of
the tread face. In the tread face shown in FIG. 3, the contours of
the contact faces of the plurality of protruding blocks B and the
contours of the recessed grooves are illustrated.
[0037] The tire shape inspection device 1 according to this
embodiment detects a change in height data (diameter change data of
tire radius) indicating the height of such a tread face over the
entire circumference in the circumferential direction.
[0038] Then, the tire shape inspection device 1 acquires a
variation in height of each contact face of the plurality of
protruding blocks B (hereinafter, referred to as height variation
or height change), in other words, a variation in height of each
contact face in the radial direction of the tire T (undulation
along the circumferential direction), from the detected height data
of the tread face. In the tire shape inspection device 1, a "runout
value Ro" indicating the shape of the tread face of the tire T can
be acquired from the difference between the maximum value and the
minimum value of the height variation acquired as described above,
and the surface shape of the tire T is evaluated.
[0039] The general configuration and its details of the tire shape
inspection device 1 according to the embodiment of the invention
are described below with reference to FIG. 1.
[0040] As shown in part (a) in FIG. 1, the tire shape inspection
device 1 includes a tire rotator 2, a sensor unit 3, an encoder 4,
an image processing device 5, etc.
[0041] The tire rotator 2 is a rotary machine that rotates the tire
T, which is a shape inspection subject, around a rotation axis R of
the tire T, and includes a motor or the like for rotating the tire
T. The tire rotator 2 rotates the tire T at a rotation speed of,
for example, 60 rpm. The sensor unit 3 (described later) detects
the height of the tread face toward the outer side in the radial
direction of the tire T, as the height data over the entire
circumference in the circumferential direction of the tread face of
the tire T during rotation of the tire T.
[0042] The sensor unit 3 is a unit having assembled therein a spot
light irradiation portion 7 that irradiates the surface of the
rotating tire T with spot light, a camera 6 that receives the spot
light reflected from the tread face, etc.
[0043] Part (b) in FIG. 1 is an illustration schematically showing
arrangement of equipment included in the sensor unit 3.
[0044] In part (b) in FIG. 1, the Y axis indicates the width
direction of the tread face at a height detection position of the
tread face, the Z axis indicates a detection height direction
(direction of height to be detected of the tread face) from the
tread face at the height detection position of the tread face, the
Z axis is also a direction toward the outer circumference from the
center of the tire T (outer side in the radial direction) along the
radial direction of the tire T, and the X axis indicates a
direction orthogonal to the Y axis and the Z axis. That is, in the
sensor unit 3 used for the shape detection of the tread face of the
tire T, the Y axis is a coordinate axis parallel to the rotation
axis R of the tire T shown in part (a) in FIG. 1, and the Z axis is
a coordinate axis indicating a direction normal to the rotation
axis R of the tire T. The correspondence between the tire T and the
respective coordinate axes may be changed depending on a way of
supporting the camera 6.
[0045] The spot light irradiation portion 7 is equipment (device)
that includes a spot light source formed of a semiconductor laser,
a condenser lens, etc., and provides irradiation with a beam of
laser light in a direction different from the detection height
direction (Z-axis direction) at the height detection position so
that small-diameter spot light is formed on the tread face of the
tire T.
[0046] The laser light from the spot light irradiation portion 7
forms small-diameter spot light on the tread face of the tire T.
The spot light is set at a single point (prescribed position) in
the width direction of the tread face, and the tire T is rotated by
the tire rotator 2. Hence, the tread face of the tire T is scanned
with the spot light formed on the tread face over the entire
circumference.
[0047] Also, the camera 6 includes a camera lens 8, and an image
capturing device (light receiving element) 9 formed of, for
example, a CCD (charge coupled device). The camera 6 receives
reflection light (desirably, regular reflection light) of the spot
light irradiated on the tread face of the tire T, by the surface of
the light receiving element 9. A signal indicating the light
receiving position and the brightness of the reflection light at
the light receiving element 9 is output from the sensor unit 3 to
the image processing device 5.
[0048] The tire rotator 2 is provided with the encoder 4. The
encoder 4 is a sensor that detects the rotation angle of the
rotation axis R of the tire rotator 2, that is, the rotation angle
of the tire T, and outputs the detected rotation angle as a
detection signal. The output detection signal is used for
controlling the timing of reception of light (capture of image) of
the spot light with the camera 6.
[0049] For example, the image processing device 5 receives a
detection signal output from the encoder 4 every prescribed
rotation angle of the tire T rotating at 60 rpm, and controls the
sensor unit 3 so that the camera 6 captures an image of spot light
in synchronization with a reception timing of the detection signal.
Accordingly, an image of the spot light formed on the tread face
can be captured at a prescribed image capturing rate corresponding
to the reception timing of the detection signal.
[0050] By the image capturing operation for the spot light, the
signal from the sensor unit 3 can provide image data acquired by
scanning the entire circumference of the tread face (one line image
along the circumferential direction at a prescribed position in the
width direction of the tread face), and the one line image is input
to the image processing device 5.
[0051] The image processing device 5 detects height data for one
line scanned with laser light from the spot light source on the
tread face, by applying a geometrical method such as triangulation
to the input one line image.
[0052] FIG. 4 is a graph showing height data of the tread face
detected one a scanning line (height variation detection line) L1
shown in FIG. 3.
[0053] In the graph in FIG. 4, the horizontal axis indicates the
position at which a detection signal is output from the encoder 4
in one turn of the tread face, that is, the position of captured
spot light. In one turn (360 degrees) of the tread face, for
example, images of spot light are captured at image capture
positions in a range from about 1000 points to 5000 points. Also,
the vertical axis indicates the height [mm] of the tread face. That
is, the graph shown in FIG. 4 connects height data at respective
image capture positions with lines and shows the height data on the
scanning line L1 of the tread face.
[0054] With reference to FIGS. 5 to 7, processing of acquiring
height changes of the contact faces from the height data of the
tread face shown in FIG. 4, the processing which is a feature of
the invention, is described. The processing described below is
executed by the image processing device 5.
[0055] FIG. 5 is a graph showing part of the height data of the
tread face shown in FIG. 4 and surrounded by a circle M among the
height data of the tread face, in an enlarged manner. FIG. 5
indicates the height data of the tread face from an image capture
position 2100 to an image capture position 2200 in an enlarged
manner. In the graph shown in FIG. 5, the height at each image
capture position is indicated as point data, and respective pieces
of point data are connected with lines. Consequently, FIG. 5
illustrates a plurality of mountain-shaped figures.
[0056] The plurality of mountain shapes correspond to the
protruding blocks B of the tread face, and areas between the
mountain shapes correspond to the recessed grooves of the tread
face. Hence, areas around the top portions of the plurality of
mountain shapes indicate the heights of the contact faces formed at
the top portions of the respective protruding blocks B. The left
side of each mountain shape is slightly inclined as compared with
the right side.
[0057] It may be conceived that the inclination is generated
because reflection light from a side face of a protruding block B
facing a groove is detected with the camera 6 instead of reflection
light from a contact face of the protruding block B, and hence a
height at a low position other than the contact face of the
protruding block B is detected. In addition to the height of the
side face of the protruding block B, a spew or a burr higher than
the contact face may be occasionally detected. That is, the height
data of the tread face shown in FIGS. 4 and 5 contain a height of a
portion other than the contact face.
[0058] Owing to this, the image processing device 5 acquires the
height changes of the contact faces by removing height data of a
portion other than the contact faces from the height data of the
tread face, or in other words, by extracting the height data of the
contact faces (contact face acquisition step).
[0059] To be specific, a prescribed height range which is a range
of height changes of the contact faces is set by using an average
value AV of the height data of the tread face on the scanning line
L1 shown in FIG. 4, and a dispersion .sigma.2 or a standard
deviation .sigma. which is a characteristic of a distribution of
the height data of the tread face. In this embodiment, a prescribed
height range having a width that is a prescribed number of times a
standard deviation .sigma. of the height data around the average
value AV of the detected height data of the tread face is set. In
particular, the prescribed height range is a height range from
about "average value AV.+-..sigma." to "average value
AV.+-.3.sigma." by using the average value AV and the standard
deviation .sigma..
[0060] Among the height data of the tread face shown in FIG. 4, it
is assumed that the height data included in this prescribed height
range is the height data of the contact faces. Based on this
assumption, by removing a height outside of the prescribed height
range from the height data of the tread face, the height and groove
of the side face of the protruding block B, the height of a spew or
a burr being higher than the contact faces, and the like, are
removed.
[0061] Consequently, the height data of the contact faces included
in the prescribed height range is extracted (acquired) from the
height data of the tread face shown in FIG. 5, like height data
indicated in an enhanced manner with triangle marks in a graph in
FIG. 6.
[0062] As shown in FIG. 6, after the extraction of the height data
of the contact faces, the image processing device 5 acquires the
height changes of the contact faces by interpolating heights
removed because the heights are outside of the prescribed height
range in the contact face acquisition step, by using heights in the
prescribed height range and smoothing the heights, for the
extracted height data of the contact faces (height change
interpolation step).
[0063] To be specific, neighboring pieces of height data are
connected with lines for the respective extracted pieces of height
data. At this time, a line connecting neighboring height data
indicates height data included in the prescribed height range
defined by the average value AV and the standard deviation .sigma..
At the same time, the line is for linearly interpolating the height
data removed because the height data is outside of the prescribed
height range in the contact face acquisition step.
[0064] Further, in the height change interpolation step, the image
processing device 5 smoothens the height changes of the tread faces
acquired by such linear interpolation by using, for example, a
low-pass filter of, for example, about 4-th order to 16-th order.
Hence, the image processing device 5 acquires a curve indicating
height changes of the contact faces on the scanning line L1.
[0065] FIG. 7 shows a graph in which a curve indicating the height
changes of the contact faces on the scanning line L1 acquired in
the height change interpolation step is overlaid on the height data
of the tread face shown in FIG. 4. As shown in FIG. 7, the curve
indicating the height changes of the contact faces acquired through
the contact face acquisition step and the height change
interpolation step also indicates the height changes of the contact
faces of the tire T.
[0066] Then, the image processing device 5 detects the maximum
value and the minimum value in the curve of the acquired height
changes of the contact faces, and acquires the difference between
the detected maximum value and minimum value as a runout value Ro
indicating the shape of the tread face (runout value acquisition
step). By evaluating the magnitude of the acquired runout value Ro,
the shape of the tread face of the tire T can be inspected.
[0067] Also, a local height change of the contact face on the
scanning line L1 is evaluated, so that a bulge or a dent which may
increase the rolling resistance of the tire T can be detected. To
be specific, the height changes of the tread face before smoothing
acquired in the height change interpolation step are smoothed by
using a low-pass filter of, for example, about 20-th order to
100-th order, and the smoothed height changes of the contact faces
are multiplied by a window function such as a rectangular window.
In the smoothed height changes of the contact faces, by multiplying
a waveform corresponding to 7 degrees of the rotation angle of the
tire T by, for example, a window function such as a rectangular
window, a Bulge/Dent value being a local runout value on the
scanning line L1 is acquired, and a local height change of contact
faces can be evaluated.
[0068] The window function used at this time is not limited to a
rectangular window and may desirably select a window function
corresponding to a measurement result desired to be obtained. Also,
while the range cut by the window function is for 7 degrees in
terms of rotation angle of the tire T, the range may be set for an
angle corresponding to a measurement result desired to be
obtained.
[0069] By executing the above-described steps, the runout value and
Bulge/Dent value of the tread face on the scanning line L1 are
acquired. However, if the height data of the tread face is acquired
on the scanning line L1 a plural number of times, the same result
as the height data of the tread face shown in FIG. 4 may not be
always obtained. Ideally, in the tire shape inspection device 1, it
is desirable to acquire a runout value and a Bulge/Dent value on a
scanning line on which the same result can be always obtained.
[0070] Hence, height data of the tread face is acquired a plural
number of times on each of a plurality of scanning lines in the
width direction of the tread face, and the degrees of variations of
a plurality of acquisition results are evaluated in terms of
reproducibility of a measurement result. To be specific,
reproducibility of a measurement result on each scanning line is
evaluated by using the dispersion .sigma.2 or the standard
deviation .sigma. used in the contact face acquisition step.
[0071] FIG. 8 is a graph indicating reproducibility of a
measurement result when about 200 scanning lines are set in the
width direction of the tread face, and 10 height changes are
acquired on each scanning line. The graph in FIG. 8 shows a
variation width of the standard deviation .sigma. in height data
for 10 times on each scanning line. That is, a scanning line with a
large variation width of the standard deviation .sigma. has low
reproducibility of the measurement result. Hence, such a scanning
line is not appropriate for acquisition and evaluation of the
runout value and Bulge/Dent value.
[0072] In the graph in FIG. 8, the scanning line L1 described in
this embodiment has a small variation width of the standard
deviation .sigma., and reproducibility of the measurement result is
high. Hence the scanning line L1 can be a scanning line appropriate
for acquisition and evaluation of the runout value and Bulge/Dent
value. As described above, the reproducibility of the plurality of
scanning lines may be preferably evaluated, and then a scanning
line with the highest reproducibility may be used for the shape
inspection of the tread face.
[0073] Further verifying the graph in FIG. 8, on a scanning line
that passes an edge portion (edge) of a protruding block, the
variation width of the standard deviation .sigma. may be large and
the reproducibility of the measurement result is low. In
particular, if the edge of the protruding block is close and
parallel to a scanning line, the reproducibility of the measurement
result on the scanning line is extremely low.
[0074] Owing to this, boundary lines, which are the contours of the
protruding blocks (that is, edge portions of the protruding blocks)
are detected, and mask processing is executed on the boundary
lines. That is, a mask image indicating the positions of the
boundary lines of the protruding blocks is generated (mask image
generation step). In this mask image generation step, while the
sensor unit 3 includes a line light irradiation portion that
irradiates the tread face with sheet light and an area camera that
captures an image of line light formed on the tread face,
triangulation is applied to the captured image of line light and an
area image indicating a bulge and a dent of the tread face of the
tire T is acquired. Accordingly, the boundary lines (i.e., edge
portions of the protruding blocks), which are the contours of the
protruding blocks can be detected.
[0075] To be specific, by masking the image of the tread face
captured as an area image with the mask image generated in the mask
image generation step, the section of the boundary lines of the
protruding blocks is masked. The contact face acquisition step
using the prescribed height range with the average value AV and the
standard deviation .sigma. is applied to the entire masked area
image of the tread face, and the height changes of the contact
faces are detected. Then, by applying the above-described height
change interpolation step and runout value acquisition step to the
detected height changes of the contact faces, not the runout value
or the Bulge/Dent value on the single scanning line, but the runout
value and the Bulge/Dent value of the entire tread face can be
acquired.
[0076] The method of generating the mask image, the method of
applying the mask image to the area image of the tread face, and
the method of detecting the height changes from the masked area
image may use, for example, methods disclosed in Japanese
Unexamined Patent Application Publication No. 2011-141260 the
applicant of which is the same as that of this application.
[0077] The embodiment currently disclosed is merely an example for
all the described points, and does not intend to give limitations.
In particular, regarding matters not explicitly disclosed in the
currently disclosed embodiment, for example, an operation condition
and a measurement condition, various parameters, dimensions, a
weight, and a volume of a structure, the embodiment employs values
within a range normally implemented by those skilled in the art and
being able to be easily expected by those skilled in the art.
[0078] This application is based on Japanese Patent Application
(Japanese Patent Application No. 2012-194205) filed Sep. 4, 2012,
which is hereby incorporated by reference herein in its
entirety.
REFERENCE SIGNS LIST
[0079] 1 tire shape inspection device
[0080] 2 tire rotator
[0081] 3 sensor unit
[0082] 4 encoder
[0083] 5 image processing device
[0084] 6 image capturing camera
[0085] 7 spot light irradiation portion
[0086] 8 camera lens
[0087] 9 image capturing device
* * * * *